add ability to override compile command in generated req file

README.md

@@ -94,6 +94,28 @@ If you use multiple Python versions, you can run ``pip-compile`` as ``py -X.Y
 -m piptools compile ...`` on Windows and ``pythonX.Y -m piptools compile ...``
 on other systems.
 
+Configuration
+-------------
+
+You might be wrapping the pip-compile command in another script. To avoid confusing
+consumers of your custom script you can override the update command generated at the top of
+requirements files by setting the `CUSTOM_COMPILE_COMMAND` environment variable.
+
+```console
+$ CUSTOM_COMPILE_COMMAND="./pipcompilewrapper" pip-compile requirements.in
+#
+# This file is autogenerated by pip-compile
+# To update, run:
+#
+#    ./pipcompilewrapper
+#
+flask==0.10.1
+itsdangerous==0.24        # via flask
+jinja2==2.7.3             # via flask
+markupsafe==0.23          # via jinja2
+werkzeug==0.10.4          # via flask
+```
+
 Example usage for `pip-sync`
 ============================
 

piptools/writer.py

@@ -34,18 +34,22 @@ def write_header(self):
             yield comment('# This file is autogenerated by pip-compile')
             yield comment('# To update, run:')
             yield comment('#')
-            params = []
-            if not self.emit_index:
-                params += ['--no-index']
-            if not self.emit_trusted_host:
-                params += ['--no-emit-trusted-host']
-            if not self.annotate:
-                params += ['--no-annotate']
-            if self.generate_hashes:
-                params += ["--generate-hashes"]
-            params += ['--output-file', self.dst_file]
-            params += self.src_files
-            yield comment('#    pip-compile {}'.format(' '.join(params)))
+            custom_cmd = os.environ.get('CUSTOM_COMPILE_COMMAND')
+            if custom_cmd:
+                yield comment('#    {}'.format(custom_cmd))
+            else:
+                params = []
+                if not self.emit_index:
+                    params += ['--no-index']
+                if not self.emit_trusted_host:
+                    params += ['--no-emit-trusted-host']
+                if not self.annotate:
+                    params += ['--no-annotate']
+                if self.generate_hashes:
+                    params += ["--generate-hashes"]
+                params += ['--output-file', self.dst_file]
+                params += self.src_files
+                yield comment('#    pip-compile {}'.format(' '.join(params)))
             yield comment('#')
 
     def write_index_options(self):